Peter Parker, Eat Your Heart Out

The US army is looking at using spider silk generated from genetically modified silkworms:

Spider silk is one of nature’s toughest substances, similar in strength to the Kevlar plastic found in bulletproof vests but much more flexible. Kraig Biocraft, a company out of Ann Arbor, Michigan, genetically altered silkworms to produce a fiber that’s similar to pure spider silk. Today, they announced an Army contract to test this so-called Dragon Silk for possible use in body armor.

There’s a reason that silk from worms is cheap but you can’t buy pajamas made from spider fabric: spiders are territorial and cannibalistic, which makes farming them for fabric production almost exorbitant.

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The technology behind Dragon Silk is based in part on the work of Malcolm J. Fraser, Donald L. Jarvis, and their colleagues. As they explain in this paper, they introduce specific pieces of spider DNA into silkworm eggs, creating an entirely new type of silkworm that can spin spider silk.

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Rice doesn’t anticipate that Dragon Silk will be a direct replacement for Kevlar, which has a strength of 3 gigapascals. [425,000 psi] Spider silk has a strength of 2 gigapascals, [290,000 psi] only about two-thirds as strong.

“But Kevlar has an elasticity of 3 percent,” says Rice. “If you have a Kevlar fiber, it’s not going to move at all. Our fibers have a 30 to 40 percent elasticity before they break.”

FWIW, the additional deformation that spider silk can take means that it is absorbing a lot more energy than the Kevlar.  (The very crude sketch depicts energy as the area under the various curves)

I am not sure of how spider silk could be used in a structural context, but given my experience with the material, it's relatively low modulus would indicate that any design would be driven by stiffness issues rather than strength issues, which would make it rather similar to handle to fiberglass.